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Dear all,
here is my schematic
my PCB design is close to DEM-OPA-SOT-1A
Input is a photomultiplier tube . its parasite capacitance i estimate is 20-30pF ,and so i choose C5=0.25pF.
Oscillation problem:
I found that it has something to do with the line position (the phenomenon still exists after changing the coaxial line).
the signal generator you can see it as a DC voltage for LED
at first 3.37V ,output is OK
Change to 3.39V
You can see that when the amplitude is close to 300mV (200mV/div), the oscilloscope(50ohm) waveform is oscillation
the red circle is output coaxial line
still 3.39V
after i adjusted the position of the coaxial line, output is OK without oscillation
i think it has something to do with my TIA.
Please help me solve this problem.
DC bias:
the first time i use my TIA ,its offset is 20-30mV（too big）, after few hours ,the offset is around 0mV（this is what i want, and lucky this does not change for a week）. i wonder if this phenomenon is normal or my TIA has some problem. i also wonder the reason why the offset change from big to nearly 0mV .
Regards,
Hou Guanting
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